Insolubilization of water-soluble cellulose ethers



Patented Feb. 27, 1945 INSOLUBILIZATION OF WATER- SOLUBLE CELLULOSEETHEBS Shailer L. Bass, Richard M. Upright, and Firth L. Dennett,Midland, Mich., assignors to The Dow Chemical Company, Midland, Mich, acorporation oi Michigan No Drawing.8

8 Claims.

This invention relates to a method of insolubilization of water-solublecellulose ethers, whereby such ethers are made to be insoluble inorganic solvents and substantially insoluble in water. It relates inparticular to such a method applied to methyl cellulose of thewater-soluble Application August 7, 1941, erial No. 405,786

article, whether it be free film, filament or a coating on paper, cloth,or like flexible base. Thus, for abrasion-resistance of the article andfor simplicity and economy of operation in producing the same, it may bedesired to use a water solution or a water-soluble cellulose ether. Itmay, at the same time, be desired to have the finished articleinsoluble, or substantially so, in water and insoluble in organicsolvents. Further, it may be desired that the cellulose ether in thefinished article exhibit flexibility and possess a degree of claritycomparable with the corresponding properties of the customaryorgano-soluble cellulose ethers which might be used for analogouspurposes.

It is, accordingly, an object of the invention to provide a methodwhereby water-soluble. cellulose ethers may be employed in, or appliedfrom, water solution and then insolubilized, both as regards water andorganic solvents, by simple converted to an insoluble form. Other andrelated objects will appear hereinafter.

In a prior filed application, Serial 358,423, filed September 26, 1940,and now U. S. Patent No. 2,270,180, two of the present inventors havereported that the foregoing objects may be attained through the use, asan insolubilizingagent, of a water-soluble'polyhydric alcohol modifiedurea formaldehyde resin to be added to a water solution oi awater-soluble cellulose ether. According to the said prior application,films deposited from such solution when dried and baked areinsolubilized with respect to organic solvents and aresubstantially'insolubilized with respect to water.

According to the present invention, insolubilization of water-solublecellulose ethers may be attained to a greater extent than by the methodof the above-identified prior application, by forming a water solutionof a water-soluble cellulose ether and a water-soluble andheat-hardenable melamine resin, particularly a water-soluble melaminealdehyde resin, forming a 111m or filament from the solution, thendrying and heating the same. More particularly, films, filaments, andthe like, which are insoluble in organic solvents and. substantiallyinsoluble ih water, are prepared by adding from 2 to 15 per cent, andpreferably from 5 to 15 per cent, based on the total weight of solidspresent, of a melamine resin in water solution to a water solution of awatersoluble cellulose ether, preferably, though not necessarily,adjusting the pH of the resulting solution to a range of 4 to 5, andforming the above-mentioned films, filaments, or the like, from thisresulting solution. After drying in air at room temperature thestructure obtained is heated for at least 5 minutes and ordinarily fornot more than minutes to a temperature preterably in the muse from to C.This treatment provides a highly flexible article which is substantiallyinsoluble in water and in the common organic solvents. As will be shownhere inaiter the articles produced according to the present method are,for any given proportion of ingredients and time and temperature oftreatment, more resistant to water than are those described in theabove-identified co-pending .application.

The cellulose ethers here concerned are any which are soluble in waterand include such products as, for example, water-soluble methylcellulose, water-soluble hydroxy-ethyl cellulose, and the water-solublealkali salts and ammonium salt of cellulose glycolic acid. It is, ofcourse, well known in the art that the water-soluble cellulose etherscontain in general more etherifying group per Cs unit than do thealkali-soluble cellulose ethers and they contain fewer etherifyinggroups per Co unit than do the corresponding organic solvent-solublecellulose ethers. The invention is directed to a treatment of thoseethers of cellulose which are capable oi remaining in solution in waterwithout the use of strong alkalies.

Among the melamine resins which may be used melamine formaldehyderesin'which has been found to be satisfactory for use in the presentinvention and to be typical in its behavior of all of the water-soluble,heat-hardenable melamine resins with which we are familiar, is givenherewith.

35 per cent aqueous formaldehyde at a pH of approximately 8 in aqueousmedium containing 7 mols (a slight excess) of iormaldehyde. Thecondensation is carried out at a temperature of 45 to 60 C. at a reducedpressure of about 100 millimeters absolute. The reduced pressure ismaintained until about 70 to 80 per cent of the water originally presentand of that formed during the reaction has been removed. The resultingpartly dehydrated mass has a viscosity of about 100 poises. This viscousproduct is then heated to 90 C. in the course of about one hour in thepresence of a slight'excess overthe theoretical 3 mols of diethyleneglycol. The temperature is gradually raised to about 120 C. in thecourse of about 5 hours and the mixture held at this temperature atatmospheric pressure until, the desired water-solubility of the melamineformaldehyde condensate is obtained. When this stage is reached thereremains in the reaction vessel about 810 grams of resin solution ofabout 50 per cent concentration for each gram-molecular weight ofmelamine used. Representative batches of the above-described resin havehad the following average properties:

Viscosity (Gardner-Holt at 25 C.) W-X Acid number 0.13 Solventtolerances:

Diethyiene glycol Ethylene glycol.-. Infinite tl i 1 al h l e coMonoliutyl ether of diethylene glycol 300 Ethyl alcohol do 200 Mineralspirits None In a preferred method of carrying out the invention thereis added to a water solution of 1 Preferred, andgenerally operativetemperatures,

are those from 105 to 110 C. The lower temperatures require somewhatlonger times to arrive at an insoluble product than do the highertemperatures within the recited range. The soheated articles aresubstantially insoluble in water and are insoluble, as well, in mostcommon organic solvents. I

The suggested amount of melamine resin is about to 15 per cent of thecombined weight of that resin and the methyl cellulose. This rangeofproportions gives the most advantageous results. Lesser amounts ofmelamine resins such as, for example, from 2 to 5 per cent may beemployed. If much less than about 2 per cent of the melamine product isincorporated in the methyl cellulose it is found that no practicalamount of heating will give a water-insoluble amass? 1 mol of melamineis caused to condense with To illustrate the effect of heating time onthe insolubilization of methyl cellulose with a watersolublemelamine-formaldehyde condensate such as that whose prepa ation isdescribed in detail above, the following table is given. The methylcellulose employed was one whose 2 per cent solution in water has aviscosity of about 50 centipoises. Films were cast from the solutions,and were dried at room temperature. The films were then heated to105-110 C. forthe time interval shown in the table. .The so-heated filmswere weighed and were then immersed in water for 48 hours at roomtemperature (25-28 0.). After this treatment the film, when notcompletely dissolved, was removed from the water, dried andre-weighed'to determine the loss inweight, from which was computed theper cent watersolubility reported in the table. Water-solubility of thedeposited and heated films was determined by immersion of the weighedsamples in water for 48 hours at 10m temperature (25"- 28 C.) re-dryingand weighing.

Table 1 Per cent water-solubility, melamine-tormaldehyde condensate.Time in minutes at l05-ll0 0. per cent n 100 38.8 5 85.6 22.9 in 49.920.0 50.6 15.9 00 48.0 14.7

A further comparison was made between the effect of the above-recitedconditions of treatment on a methyl cellulose-melamine condensatecomposition containing 2.5 per cent of the condensate, and a methylcellulose-urea-formaldehyde condensate of the water-soluble typecontaining'the same methyl cellulose and 13 per cent of theglycol-modified urea-formaldehyde.

Table 2 Per cent water-solubility Methyl cellulose, 97.5 melaminecondensate, 2.5

Methyl cellulo 87 urea-formaldehyde, l3

It is observed that 2.5 per cent of a water-soluble melamineformaldehyde condensate is fully as efiective as an insolubilizing agentfor methyl cellulose under the moderate temperature conditions employedas is 13 per cent of a watersoluble glycol-modified urea-formaldehydecondensate, such as is described in the above-identified priorapplication, No. 358,423. It is further pointed out that much lowertemperatures are dltions is obtained when the films are depositedrequired to produce a given low solubility rating on the films of thepresent invention than to produce an equivalent low solubility from afilm containing a like amount of the insolubilizing agent of the saidprior application.

Films were prepared containing sui'licient or a water-soluble melamineformaldehyde condensate and of the glycol-modified urea-formaldehydecondensate of the prior application to have solu- '-bility values ofabout 15 to 25 per cent when heated at 105 C. for 30 minutes.Flexibility oi the heated films was determined on the M. I. T. foldingendurance tester using a tension oi 1500 grams and a test strip 15millimeters wide.

Table 3 Water solubility m Composition film TlmeoilleatingTimeoilleating min. 30min. 5min. 30min.

Men: 1 cellulose, 877.-.-.- 1 &,{l $3 ,35 26 17 301 114 0 cc ose, 2 ggia gl gl g 69 49 173 121 e co ose, 3 {Urea-zlrmaidehyde,25%.. 23 38 Itis observed that the compositions of the present invention are morefiexible than those previously described. When comparing films of equalresin content (Nos. 1 and 2), that of the present invention is 74 percent more flexible than that of the prior application, when both areheated at 105 C. for 5 minutes, and has the same flexibility, withinexperimental error, after 30 minutes heating. The film of thisinvention, heated for 30 minutes, is only about 32 per cent as solublein water as that of the comparative composition.

When comparing films (Nos. 1 and 3) of approximately equal ultimatewater-solubility, in Table 3, above, that oi the present invention is400 per cent more flexible after only 5 minutes at 105' C. than is thecomparative film, and is 200 per cent more flexible after 30 minutesheatin: at the same temperature.

The methyl cellulose 01' the foregoing examples has been given purely asan example or a water-soluble cellulose ether. In like manner to thatdescribed, a film, deposited from a water solution of 80 parts ofhydroxy-etbyl cellulose and 20 parts of a water-solublemelamine-formaldehyde condensate, was only 30 per cent soluble in waterwhen heated at 105 C. for 15 minutes, as compared with a value of about95 per cent solubility for the freshly deposited, air-dried but unheatedfilm. Similarly, a water solution of 80 parts of sodium celluloseglycolate and 20 parts of a water-soluble melamine-formaldehydecondensate gave films which, when heated to 105 C. for 15 minutes, wereonly 35 per cent soluble in water under the standard test conditions, ascompared with 100 per cent solubility for the air-dried but unheatedfilm.

In addition to the decrease in solubility in water characterizing theheated films oi the present invention, these films are completelyinsoluble in mineral spirits, and substantially so in most commonorganic solvents.

Substantially insolubility is obtained when the films, heated asdescribed, are cast from neutral or even from slightly alkalinesolutions, but maximum insolubility under any given heating confromsolutions having pH of from 4 to 5. A suitable acidulating agent forObtaining this pH and for accelerating the insolubilization reaction isphosphoric acid, though other acids, such as citric acid, oxalic acid,and the like, are also suitable.

The particular water-soluble melamine resin described in detail is acondensate of melamine,

furaldehyde, and the like, modified subsequent to the initialcondensation, if necessary, with glycol, glycerol, diethylene glycol, orother polyhydric alcohol. 50 long as the melamine resin isheat-hardenable and is soluble in water, it is included in the scope ofthe present invention, regardless of its specific composition.

The invention may be used to convert watersoluble cellulose ethers towater-insoluble products other than the films herein described. Thus, itmay apply to filaments, tapes, or coatings provided that the coatedarticle can withstand the temperature employed when heating the film toproduce insolubility. When operating in th preferred ranges ofproportion, time, and temperature, the treated films are fiexible,substantially insoluble, and are practically free from discoloration.

In the foregoing description, reference is had to the addition of themelamine resin to the aqueous cellulose ether solution. It is to beunderstood that an equivalent operation, and one intended to be includedin the scope of the claims, comprises dissolving a water-solublecellulose ether in an aqueous solution of a melamine resin. Yet anotherequivalent operation is the mixing of water solutions of the twoingredients.

We claim:

1. The method which includes: forming a water solution oi awater-soluble cellulose ether and a water-soluble, heat-hardenablemelamine-aldehyde resin which has been modified by condensing with apolyhydric, alcohol, said resin being present in an amount of from'2 to15 per cent of the total weight of resin and cellulose ether; vaporizingthe water from the solution and heating the dry composition remaining ata temperature between about and C. for a period correspondingly in therange from about 60 to about 5 minutes, sufilcient substantially toinaolubilize the dried composition.

2. The method as claimed in claim 1, wherein the melamine resin is amelamine formaldehyde resin in amount from 5 to 15 per cent of the totalweight oi resin and cellulose ether.

3. The method which includes: forming a water solution of awater-soluble methyl cellulose and a water-soluble heat-hardenablemelamine-formaldehyde-glycol condensate, said condensate being presentin an amount from 5 to 15 per cent of the total weight of resin andmethyl cellulose; vapor-v izing the water from th solution; and heatingthe dry composition remaining at a temperature between about 90 and 170C. for a period correspondingly in the range from about 60 to about 5minutes, suflicient substantially to insolubilize the dried composition.

4. The method as claimed in claim 1, wherein there is added to the watersolution a. small amount of acid suflicient to adjust the pH to about 4to 5. i

5. The method as claimed'in claim 1, wherein the cellulose ether iswater-soluble methyl cellu- I ture 6. The method as claimed in claim 1,wherein the dried article is heated to a temperature between about 105and 110 C. for a period substantially to insolubilize the same. 'l. Themethod which includes forming a water solution of a water-solublecellulose. ether and a period correspondingly in the range from about 60to about 5'minutes, sumcient substantially to insolubilize the driedcomposition.

8. A substantially water-insoluble thermal reaction product of awater-soluble cellulose ether and a water-soluble heat-hardenablemelaminealdehyde-polyhydric alcohol condensate wherein th condensate ispresent in an amount or from 2 to 15 per cent of the total weight ofcondensate and methyl cellulose, said reaction product being identicalwith that obtained according to the method of claim 1.

4 SHAH-ER L. BASS.

RICHARD M. UPRIGHT. FIRTH L. DENNE'I'I.

